Process for desulphurization of petroleum oil

ABSTRACT

A process for desulphurization of petroleum oil, comprising the step of diluting the feed oil with a suitable organic solvent prior to the desulphurization reaction, is disclosed. The organic solvent is selected from alkanes, alkenes, cyclic alkenes and alkynes, and particularly selected from n-hexane, cyclohexane, heptane, pentene, hexene, heptene, octene, toluene and xylene. The solvent concentration in the mixture of feed oil and solvent is in the range of 0.1-70%.

FIELD OF DISCLOSURE

The present disclosure relates to desulphurization processes.Particularly, the disclosure relates to a process for desulphurizationof petroleum heavy oils and residual petroleum oils, more particularlycarbon black feed oil.

BACKGROUND

Petroleum oils are complex mixtures of primarily hydrocarbons and othercarbon containing compounds. The overall composition of the petroleumoil or crude oil is known to vary significantly from its origin orgeographical location of the refinery. The elemental composition ofthese oils consists of about carbon (84-87%), hydrogen (12-14%) alongwith oxygen, nitrogen, sulfur, moisture and ash. The sulfur content mayvary substantially from 0.2-8%. In addition to these main components,there are traces of metal impurities, that may be present initially orget associated with the oil during various refinery processing steps.The crude oils may also contain hydrocarbons, paraffins, asphaltenes,resins and ash. The crude oil compositions can be differentiated intovarious individual fractions at different boiling ranges. The lowboiling fractions (<170° C.) are typically napthas, those between180-250° C. are kerosene and the ones boiling in the range of 250-350°C. are termed as gas oils. The fractions boiling above 350° C. aregenerally termed as residues and are obtained after all or most of thedistillable products have been removed from the petroleum oil. Theseresidue fractions could be further distinguished as light vacuum gasoils, heavy vacuum gas oils and vacuum residues. Each of these differentfractions has different molecular distribution of various hydrocarbonspecies and related compounds. In particular, one of the significantaspects is the distribution of sulfur containing species in thesefractions. The use of the petroleum oil residues includes heating (as afuel), and as a feedstock for the manufacture of carbon black. Thepresence of sulfur in the petroleum oil residue has a number ofshortcomings. During the complete or partial combustion of the petroleumresidue, sulfur gets converted to SO₂ and SO₃. These cause majorenvironmental issues in the form of acid rains and adversely affecthealth. Further, the sulfur species cause poisoning of catalyst systemsused in the refineries. These are also known to be the primary cause ofcorrosion of equipments and exhaust. The presence of sulfur in theresidue fraction has further ramifications in case of use of this as rawmaterial for carbon black manufacturing. Apart from significant airpollution, these species remain associated with the final carbon blackproduct which is detrimental to various applications. Furthermore, highsulfur content affects the throughput of the manufacturing process.

Carbon black feed oil (CBFO) is a raw material used for manufacturingcarbon black, an important material used in the tyre industry. Carbonblack feedstock is a mixture of C₁₂ and higher components rich innaphthalene, methylindenes, anthracene, fluorene and other poly-aromaticcomponents. CBFO is essentially procured either from oil refineries orfrom coal tar distillers. There are two types of CBFO viz. High BMCItype and General type. “BMCI” (Bureau of Mines Co-relation Index)effectively measures the degree yield of carbon black. Higher the BMCI,better the yield of carbon black. High BMCI CBFO is used as a rawmaterial by carbon black manufacturers while the other grade is used byvarious consumers to manufacture rubber process oils, incense sticksetc.

Sulfur content in CBFO reduces the effective BMCI value. Moreover, thissulfur gets carried to the final carbon black product as an impurity.Hence, it is of interest to reduce the sulfur content of the CBFO.Hence, it would be of interest to discover a method for reducing thesulfur content of the petroleum oil residue to be used as CBFO.

A desulphurization process is usually carried out to remove sulfur (S)from natural gas and petroleum products such as gasoline or petrol, jetfuel, kerosene, diesel fuel and fuel oils. The refinery feedstock(naphtha, kerosene, diesel oil and heavier oils) contains a wide rangeof organic sulfur compounds, including thiols, thiophenes, organicsulfides, disulfides and many others. These organic sulfur compounds arethe products of degradation of sulfur containing biological components,present during the natural formation of the fossil fuel, petroleum crudeoil. The purpose of removing sulfur is to reduce sulfur dioxide (SO₂)emissions that result from using these fuels in automotive vehicles,aircrafts, railroad locomotives, ships, gas or oil burning power plants,residential and industrial furnaces, and other forms of equipment usingfuel for combustion.

A number of techniques including catalytic transformation processes suchas hydrodesulfurization and physico-chemical processes such as solventextraction, alkylation, oxidation, precipitation, adsorption, and thelike, have been worked in order to reduce the sulfur content fromvarious fractions of the petroleum oils. The hydro-desulfurization iscommonly used for this purpose. This process is based on catalytichydrogenation of the sulfur species to convert it into H₂S. However, thehydro-desulfurization is known to work efficiently on lower boilingfractions such as gasoline, naptha, kerosene, and the like. The catalystsystems generally include transition metals such as Ni, Co, Mo supportedon Al₂O₃. Several efforts have been made in the past to provide ahydro-desulfurization technique. Some typical prior art examples aredisclosed in U.S. Pat. No. 2,516,877, U.S. Pat. No. 2,604,436, U.S. Pat.No. 2697682, U.S. Pat. No. 2,866,751, U.S. Pat. No. 2,866,752, U.S. Pat.No. 2,911,359, U.S. Pat. No. 2,992,182, U.S. Pat. No. 3,620,968, U.S.Pat. No. 3,668,116, U.S. Pat. No. 4,193,864, U.S. Pat. No. 4,328,127,U.S. Pat. No. 4,960,506 and U.S. Pat. No. 5,677,259. Most of theseprocesses are highly suitable for treating lower boiling fractions orcrude oils. However, their efficiency drops when treating high boilingfractions or vacuum residues. This is due to the fact that lower boilingoil fractions primarily contain sulfur in the form of mercaptans orlower membered ring compounds, which are relatively easier todesulfurize. However, the high boiling fractions or resids containsulfur species that are part of the more stable ring compounds such assubstituted benzothiophenes and higher derivatives or large moleculering compounds which are extremely difficult to desulfurize. Some priorart examples for treating residues by hydro-desulfurization include U.S.Pat. No. 2,640,011, U.S. Pat. No. 2,992,182, U.S. Pat. No. 4,328,127 andU.S. Pat. No. 4,576,710. In most of the cases, the treatment parametersare extreme i.e. use of high temperatures in excess of 400° C. andpressures in excess of 1000 psig. Moreover, the desulfurizationefficiencies are low. Further, due to these difficult processingconditions hydro-desulfurization results in coke formation, leading todeactivation of the catalyst systems. In addition, thehydro-desulfurization process results in the formation of H₂S, whichagain cannot be disposed, off due its environmental concerns. This H₂Sneeds to be further treated by the Claus process at high temperature ofabout 800° C. in presence Al₂O₃ catalyst to convert to elemental sulfur.

In addition to hydro-desulfurization, there are several other techniquesthat are being explored for the desulfurization of the petroleum oils.These include oxidative, adsorptive, solvent extraction andbio-enzymatic processes. Some typical prior art examples of oxidativedesulfurization process are disclosed in U.S. Pat. No. 3,816,301, U.S.Pat. No. 3,163,593, U.S. Pat. No. 3,413,307, U.S. Pat. No. 3,505,210,U.S. Pat. No. 3,816,301, U.S. Pat. No. 3,847,800, U.S. Pat. No.6,274,785, U.S. Pat. No. 6,277,271, U.S. Pat. No. 7,144,499, U.S. Pat.No. 7,179,368, U.S. Pat. No. 7,276,152, U.S. Pat. No. 7,314,545,US20050189261, US200600226049, US20080308463 and US20090148374. Thecommon oxidizing agents used are H₂O₂ or H₂O₂ in combination with aceticacid and in the presence of an oxidizing catalyst system. In addition,tert-butyl hydroperoxide can also be used as an oxidant as it tends tobe soluble in oil. The adsorptive processes generally use absorbentssuch as clay, Al₂O₃, bauxite, transition metal oxides systems supportedon silica or alumina, zeolites, activated carbon, etc. Some typicalexamples of these processes are disclosed in U.S. Pat. No. 2,436,550,U.S. Pat. No. 2,537,756, U.S. Pat. No. 2,988,499, U.S. Pat. No.3,620,969, U.S. Pat. No. 4,419,224, U.S. Pat. No. 4,695,366, U.S. Pat.No. 5,219,542, U.S. Pat. No. 5,310,717, U.S. Pat. No. 6,558,533, U.S.Pat. No. 6,500,219, U.S. Pat. No. 7,291,259, US20030029777,US20030188993, US20060283780 and US20090000990. The solvent extractionprocesses use various solvent systems such as dimethyl formamide,dimethyl sulfoxide, phenols, dichloroethers, nitrobenzene, and the like.Some typical prior art processes are disclosed in U.S. Pat. No.2,486,519, U.S. Pat. No. 2,623,004, U.S. Pat. No. 2,634,230 and U.S.Pat. No. 3,779,895. However, most of the above mentioned processes areaimed at desulfurization of crude oils or low boiling fractions.Similarly, most of the above mentioned processes (except bio-enzymatic)are aimed at targeting and removing the entire sulfur containingmolecule rather than removal of the sulfur atom specifically. This maynot have a significant effect while considering desulfurization of crudeoil or lower boiling fractions as the net sulfur content is less andalso the sulfur would be distributed over small number of low moleculeweight compounds. However, in case of resids where the sulfur contentcan be as high as 4-5%, the sulfur appears to be essentially distributedover a majority of the molecules contained in the oil. Thus, removingthe entire sulfur containing molecule would result in substantialmaterial loss of the oil part.

Another such desulfurization process is based on the use of alkalimetal, especially sodium metal as the desulfurizing agent. In thisprocess, the sulfur is primarily removed as a metal sulfide instead ofthe removal of the entire sulfur containing molecule. Some typical priorart examples of this process are U.S. Pat. No. 1,938,672, U.S. Pat. No.1,952,616, U.S. Pat. No. 2,902,441, U.S. Pat. No. 3,004,912, U.S. Pat.No. 3,093,575, U.S. Pat. No. 3,617,530, U.S. Pat. No. 3,755,149, U.S.Pat. No. 3,787,315, U.S. Pat. No. 4,003,824, U.S. Pat. No. 4,120,779,U.S. Pat. No. 4,123,350, U.S. Pat. No. 4,147,612, U.S. Pat. No.4,248,695, U.S. Pat. No. 4,437,980, U.S. Pat. No. 6,210,564, U.S. Pat.No. 7,192,516, U.S. Pat. No. 7,507,327, U.S. Pat. No. 7,588,680. Thesedocuments thus describe the desulfurization of crude oils and resids bysodium metal. The sodium metal can be used as pure metal or in an alloy,supported on inert species, or as dissolved in solvent such as ammonia.Also, these processes use hydrogen at high pressures in combination tothe sodium metal for desulfurization. In some processes, sodium-basedcompounds such as NaHS, NaNH₂, and the like, are used for thedesulfurization. A major product formed as a reaction of the sodiummetal with the sulfur in the feed oil is sodium sulfide (Na₂S). Some ofthe above-mentioned prior art documents also describe the regenerationof sodium from Na₂S. These processes report the effectiveness ofdesulfurization of recalcitrant sulfur especially from that of highboiling resid oils. However, these sodium-based desulfurizationprocesses are associated with limitations such as low yield ofdesulphurized feed oil, formation of large amount of insoluble sludge,requirement of hydrogen and safety concerns. The inherent high viscosityof heavy oils and petroleum residues makes it difficult for theprocessing and separation operations before and after thedesulphurization process. A large amount of valuable residual feed oilremains associated with the precipitated sodium sulfide residue or theunreacted sodium in the form of a highly viscous sludge. Also, thesludge is extremely difficult to filter and separate due to its inherentviscosity and sticky nature. Thus, there is a substantial loss of feedduring the process, especially during filtration or separation.Furthermore, due to lower density of sodium metal as compared to that ofthe residual oil, the sodium metal may tend to float at the surface ofthe oil and may lead to a hazardous situation during failed reactions orduring incomplete mixing.

Thus, the known desulphurization processes are associated with a numberof limitations such as low yield of desulphurized feed oil, formation oflarge amount of insoluble sludge, requirement of hydrogen and safetyissues. The inherent high viscosity of heavy oils and petroleum residuesmakes it difficult for the processing and separation operations beforeand after the desulphurization process. A large amount of valuableresidual feed oil remains associated to the precipitated sulfur residueor unreacted sodium in the form of a highly viscous sludge. Also, thesludge is extremely difficult to filter and separate due to its inherentviscosity and sticky nature. There is a substantial loss of feed duringthe process, especially during filtration or separation. Further, it wasobserved that the sodium-based desulfurization processes result inretention of sodium metal in the oil. The presence of sodium metal, evenat concentration as low as <100 ppm, results in change in the morphologyof the carbon black during the manufacturing processes. Therefore, thereis felt a need to develop a process to minimize the loss of feed duringdesulphurization of petroleum oils. The present invention is an improvedprocess for petroleum oil desulphurization, especially carbon black feedoil (CBFO) desulfurization, which reduces the sulfur content in the oil.

Objects

An object of the present disclosure is to provide a process fordesulphurization of carbon black feed oil which provides improved yieldand high quality of desulphurized oil.

Another object of the present disclosure is to provide a process fordesulphurization of carbon black feed oil with improved processing andhandling operations.

Yet another object of the present disclosure is to provide a process fordesulphurization of carbon black feed oil without the use of hydrogen.

Another object of the present disclosure is to provide a process forfurther treatment of the desulfurized oil for removal of the residualsodium content.

SUMMARY

In accordance with the present disclosure, there is provided a processfor desulphurization of petroleum oils, said process comprising thefollowing steps:

-   -   diluting petroleum oil with a hydrocarbon organic solvent        selected from the group consisting of alkanes, alkenes, cyclic        alkenes and alkynes, to obtain an oil-solvent mixture, wherein        the organic solvent concentration in the oil-solvent mixture is        in the range of 0.1-70%;    -   transferring the oil-solvent mixture to a reactor vessel;    -   adding solid sodium metal to the oil-solvent mixture in the        reactor vessel, wherein the sodium concentration is between        0.1-20% of the petroleum oil concentration;    -   reacting the oil-solvent mixture with sodium at a temperature in        the range of 240-350° C. and a pressure in the range of 0-500        psig for 15 minutes-4 hours under mixing to obtain a resultant        mixture;    -   cooling and settling the resultant mixture; and    -   decanting the cooled mixture and filtering the decanted solution        of desulfurized petroleum oil.

Typically, in accordance with the present disclosure, the hydrocarbonorganic solvent is selected from a group consisting of n-hexane,cyclohexane, heptane, pentene, hexene, heptene, octene, toluene andxylene.

Preferably, in accordance with the present disclosure, the processincludes the step of purging the reactor vessel with hydrogen gas at apressure in the range of 0-500 psig.

Typically, in accordance with the present disclosure, the processincludes the step of separating the organic solvent from desulfurizedpetroleum oil by distillation.

Preferably, in accordance with the present disclosure, the processincludes the step of mixing sodium with the oil-solvent mixture in thereactor vessel by using high shear mixing by means of a mixer selectedfrom an inline mixer, a mechanical mixer, a pump around loop and anultrasonic mixer.

In accordance with the present disclosure, there is provided a processfor removing residual sodium metal, said process including the steps of:treating the desulfurized petroleum oil with 0.1-10% carboxylic acid inan organic solvent at a temperature in the range of 50-150° C. for 30minutes to 90 minutes under vigorous stirring; and filtering theresultant mixture to obtain desulfurized petroleum oil having sodiumcontent between 10-50 ppm.

Typically, in accordance with the present disclosure, the carboxylicacid is selected from acetic acid, formic acid and propionic acid.

Preferably, in accordance with the present disclosure, the organicsolvent is selected from alkanes, alkenes, cyclic alkenes, alkynes andalcohol. More preferably, the organic solvent is xylene.

In accordance with the present disclosure, there is provided a processfor removing residual sodium metal by purging the desulfurized petroleumoil with air at a temperature in the range of 30-150° C.

DETAILED DESCRIPTION OF THE DISCLOSURE

The present disclosure relates to a process for desulphurization ofcarbon black feed oil (CBFO). The feed oil (CBFO) has high viscosity atambient conditions. The process comprises diluting the feed oil with asuitable organic solvent, prior to the desulphurization reaction. Theorganic solvent can be selected from the group of hydrocarbon solventsconsisting of alkanes, alkenes, cyclic alkenes and alkynes. Similarly,other oils such as petrol, kerosene, crude oil, and the like, can alsobe used for diluting the feed oil. The organic solvent is particularlyselected from the group consisting of n-hexane, cyclohexane, heptane,pentene, hexene, heptene, octene, toluene and xylene, preferably thesolvent is xylene. The solvent concentration used is in the range of0.1-70%, preferably in the range of 0.1-50%, more preferably in therange of 1-30%, in the mixture of CBFO and solvent.

The feed to the process of the present disclosure is carbon black feedoil having a sulfur content in the range of 0.1% -20%. The process ofthe present disclosure can also be used for petroleum oils of variousboiling fractions. Further, the process of the present disclosure can beused to desulphurize coal tar, shale oil or other organic sulfur bearingcompounds. The organic solvent is removed after the desulphurizationprocess. The present process results in a desulphurized stream (afterxylene removal) with a substantial viscosity reduction. The formation ofinsoluble sludge (unusable material) due to polymerization reactions ofthe desulphurized species is reduced due to improvement in the feed oilviscosity. Further, the improvement in the feed oil viscosity enhancesthe processing of the feed oils required in applications such asmanufacturing of carbon black product.

The process results in improvement of feed oil quality by means ofreducing the asphaltene content in the feed oil. Asphaltenes areconsidered as the n-heptane insoluble, toulene soluble components of acarbonaceous material such as crude oil, bitumen or coal. Asphaltenesare high molecular weight hetero-atom species that are generallyconsidered detrimental to the quality of the processed carbon blackproduct.

The process of the present disclosure is carried out in the absence ofhydrogen at a pressure in the range of 0-500 psig, this results in anhigher C:H ratio of the processed oil as compared to processes carriedin the presence of high pressure hydrogen. This is beneficial forconverting most of the processed oil into carbon black, as the hydrogenleaves the process in the form of water vapor without contributing tothe formation of product. The process removes moisture present in theCBFO. The CBFO generally contains about <1% moisture. Na metal is knownto have strong affinity to water and thereby react with moisture. Thepresent process uses sodium metal in a concentration between 0.1-20% ofthe CBFO oil concentration. Thus, moisture present in the CBFO iscompletely removed.

In one aspect of the present disclosure, the process is carried out inthe presence of hydrogen. The hydrogen added could be in the range of0-500 psig, preferably in the range of 0-300 psig, and more preferablyin the range of 0-100 psig. In addition, the hydrogen may not be presentin the form of closed system i.e. under no hydrogen pressure or apressureless system. Thus, it could be added in a continuous or a semicontinuous flow of hydrogen gas.

The process of desulphurization of the present disclosure givescrystalline sodium sulfide as the by-product. The by-product so formedis easier to separate and filter and thus results in a better recoveryof the desulfurized oil as well as better separation and processingefficiency of the desulfurized oil.

An important aspect of the present disclosure is that it provides aprocess for reducing the size of dispersed sodium—as solid particles ormolten form as droplets. Finer dispersion of sodium metal increases theefficiency of the desulphurization process. In the conventional process,the by-product, sodium sulfide tends to cover the surface of sodiummetal thereby reducing the efficiency of the process. Therefore, mixing,preferably high shear mixing, for a duration in the range of 15minutes-4 hours at a temperature in the range of 240-350° C. isprovided; high shear mixing causes the breaking of sodium sulfide andthereby provides new sodium surfaces for enhancing the reaction. Anyform of mixing may be used, such as an inline mixer, a pump around loop,a mechanical mixer, or an ultrasonic mixer, that provides the requiredamount of dispersion to the sodium metal.

In the absence of hydrogen, there is formation of insoluble sludge(unusable material) due to the polymerization reactions amongst thedesulfurized species.

Furthermore, the pure CBFO has a high viscosity of above 1500 cP atambient conditions. The process of the present disclosure results in adesulfurized stream (after xylene/solvent removal) having a substantialviscosity reduction to the range of 100-150 cP at ambient conditions.Thus, the overall effect is that the desulphurization process is carriedout in the absence of hydrogen and results in lower loss of feed oilcaused by insoluble sludge formation as well as improvement in the feedoil viscosity which is further expected to enhance the characteristicsof the processed carbon black product. Further, if the process iscarried out in the presence of hydrogen, there may be a reduction in thearomatic content of the feed due to hydrogenation (reduced C:H ratio),resulting in lower yield of the carbon black product. Thus, if theprocess is carried out in the absence of hydrogen the C:H ratio of thetreated feed would increase thereby increasing the carbon black productyield. It may be noted that the process of the present disclosure canalso be extended by means of carrying the desulphurization with Na andorganic solvent, along with hydrogen. These results with simultaneouspresence of organic solvent and hydrogen before desulphurization alsoshow benefits in terms of product quality and yield, wherein thedesulfurized feed oil yield is greater by 15-20% as against the knownprocesses. The scope of our process could thus be further extended as animproved desulphurization process involving simultaneous use of organicsolvent and hydrogen, however, in an optimized combination (or absence)of each of the reactants.

Another aspect of the process of the present disclosure is theby-product formation and processing after the desulphurization reaction.The desulphurization of feed oil using Na metal, results in theformation of Na₂S as the by-product. However, a large amount of valuableresidual CBFO is lost as it remains associated to this Na₂S residue orunreacted sodium in the form of a highly viscous sludge. The presence oforganic solvent in the feed oil prior to the desulphurization reaction,results in the formation of a crystalline and pure by-product. Thisproduct is easier to separate and filter as there is substantially lessCBFO loss. This results in a better recovery of the desulphurized oil aswell as a better separation and processing efficiency post thedesulphurization reaction.

The present disclosure uses high shear mixing apparatus aimed atreducing the size of dispersed sodium—as solid particles or molten formas droplets. This gives finer dispersion of sodium metal in the feed oilwhich increases the desulphurization efficiency of the process.Secondly, during the desulphurization process, the by-product formedtends to cover the surface of sodium metal thereby reducing theefficiency. The high shear mixing helps in breaking these surfaces andbringing new sodium surfaces for enhancing the reaction. Any form ofmixing may be used, such as an inline mixer, a pump around loop, amechanical mixer, or an ultrasonic mixer, that provides the requiredamount of dispersion to the sodium metal.

The carbon black feed oil is highly viscous with a viscosity of above1500 cP at ambient conditions. Addition of organic solvent prior todesulphurization reduces its viscosity to a substantial extent (lessthan 50 cP at ambient conditions, depending upon the amount of solventadded), making it simpler to transfer and handle as well as facilitatebetter mixing and contact with other reactants. Apart from viscosity,the density of CBFO is also high, typically between 1.01-1.08 g/cm³. Thedensity of sodium solid at 30° C. is about 0.96 g/cm³ and that of moltensodium is about 0.927 g/cm³. Thus, there is a tendency for the sodium toremain floating at the top of CBFO surface. Thus, in order to carry thereaction, it is to be ensured that the sodium remains well immersed inthe liquid, primarily by means of a continuous stirring mechanism. Thismay lead to severe safety concerns in case stirring fails or wheneverthe reaction fails. The result will be that all of the sodium (due tolow density) will rise to the top of the feed and may come in contactwith atmospheric moisture. Addition of appropriate amount of organicsolvent (say xylene having a density of about 0.86 g/cm³), lowers thedensity of CBFO to less than that of sodium and ensures that all of thesodium remains well immersed in the liquid feed at all times.

A process for removal of residual sodium metal from the desulphurizedoil is also disclosed. During the desulphurization process the sodiummetal gets finely dispersed in the oil. After the desulphurizationprocess completes, some sodium metal invariably remains in the systemeither as a suspension or bound to the molecular chain in the oil. Theseparation or removal of this sodium from the oil system is considerablydifficult by means of pure mechanical processes. The presence of thisresidual sodium even in trace quantities has serious implications on theoverall quality of product for the carbon black Industry. The process ofthe present disclosure uses acetic acid in the organic solvent mixture.The role of acetic acid is that of scavenging the sodium metal and theorganic solvent promotes a better mixing between the feedstock oil andacetic acid. Alternatively, apart from acetic acid, various carboxylicacids such as formic acid, propanoic acid, and mixtures thereof, can beused. In addition, ethanol and such alcohols can also be used forscavenging the sodium. Still further, the residual sodium removal wasalso achieved by purging the oil with air at elevated temperaturesbetween 30-150° C. Such treatment is not limited to air alone and wouldcover other gaseous agents such as oxygen, ozone, etc.

The disclosure will now be described with reference to the followingexamples which do not limit the scope and ambit of the disclosure. Thedescription provided is purely by way of illustration.

EXAMPLE 1

The experiments were carried on CBFO and xylene mixtures of varyingproportion, to evaluate the effect of xylene amount on the CBFO yield.All the following three examples (listed in TABLE 1) were carried in thepresence of hydrogen atmosphere. In example 1,150 g of CBFO was mixedwith 150 ml of xylene. This resulted in the mixture as CBFS:Xylene=50:50(weight:volume basis). The solution was mixed thoroughly and thentransferred to a high pressure reactor. 9 gm of sodium metal was weighedseparately. The sodium metal was then cut into small pieces of 0.5-1.0cm and added to the CBFS/xylene solution in the reactor. The reactorvessel was first purged with nitrogen to remove air, and then the vesselwas purged with hydrogen gas. The reactor was then pressurized up to 300psi with hydrogen. The reactor was subsequently heated to a temperatureof 290° C. The reaction was carried out at this temperature for a periodof 4 h. The entire solution was allowed to cool down to room temperatureand then the CBFO was decanted. The decanted solution was filtered outand analyzed for sulfur content by XRF (X-ray FluorescenceSpectroscopy). Similarly, the desulfurization process was carried forother varying CBFO:Xylene ratios viz. 70:30, 80:20 (as shown in examples2 and 3 in TABLE 1). The results with respect to these differentcompositions are tabulated in TABLE 1. The CBFO, xylene and sodiumcontent used is also tabulated below, along with the desulfurizationefficiency for each of the different CBFS:Xylene ratios.

TABLE 1 Amount Amount Amount of of CBFS:Xylene of CBFO Xylene ratio NaTemp. Time Desul. Pressure Ex. (g) (ml) (g:ml) (g) (° C.) (h) (%)Initial (psig) 1. 150 150 50:50 9.0 290 4 86 300 2. 210 90 70:30 13.5290 4 70 300 3. 240 60 80:20 15.5 290 4 75 300

It was observed that more than 70% desulfurization was obtained in allthe cases.

Viscosity

The sample from example 2, after desulphurization and xylenedistillation was analyzed for viscosity as a function of temperature.The sample was initially heated to about 175° C. and the viscositymeasurements were noted at different temperatures as the sample wascooled. Similarly measurements were noted for a second sample ofuntreated or raw CBFO. The results are tabulated in TABLE 2.

TABLE 2 CBFO- Untreated CBFO-Treated Sr. No Temp cP cP 1. 150° C. 20 142. 100° C. 53 23 3.  50° C. 280 70 4.  35° C. 2800 120

Thus, it was observed that a substantial reduction in the viscosity ofthe desulfurized sample especially at the lower temperature range ofbelow 50° C. was obtained. The basic advantages of viscosity reductioncould include easier processing of the oil, thereby reduction in energycost as well as improvement in quality of carbon black product due toformation of finer droplets during the nebulization process.

Asphaltene Content

The samples were further tested for the asphaltene content of the oil.Asphaltenes are found to be detrimental for the carbon black quality aswell as manufacturing processes during carbon black formation. Thus, theasphaltene content for treated oil and untreated oil was carried bydetermining the n-heptane insoluble content in both the oils. It wasobserved that the asphaltene content of untreated oil was 10.59%.However, the asphaltene content of the treated oil was substantiallyreduced to 4.65%. This indicated that our process is capable of reducingthe asphaltene content by over 50%.

EXAMPLE 2

Following experiments were carried out to optimize the time, temperatureand pressure parameters for the desulfurization process. These studieswere decided to be carried on the CBFO:Xylene ratio of 70:30. Theseoptimization studies are discussed in example 4-11 listed in TABLE 3.

TABLE 3 below describes the effect of temperature on the desulfurizationefficiency. Thus, in each case the CBFO:Xylene ratio is kept constant to70:30. The batch contained 210 g CBFO and 90 ml of xylene. 13.5 g ofsodium metal was added in each of the samples. All the reagents weretaken in high pressure reactor vessel and then pressurized with hydrogen(about 300 psig). The reactions were carried at a temperature of 290° C.with different residence time intervals of 3 h, 1 h, 45 min, 30 min and10 min for the examples 4-8, respectively. The reactor was then cooledand the CBFO was decanted and analyzed for each case by XRF. Thesedesulfurization results are tabulated in TABLE 3. It was observed thatthe desulfurization efficiency practically remains same for residencedurations of 3 h, 1 h and 45 min respectively, with overalldesulfurization efficiency of 70%. However, the desulfurizationefficiency is drastically reduced to 59 and 50% for reduced residencetime of 30 min and 10 min, respectively.

TABLE 3 Concen- tration (CBFO: Xylene) Na % Wt vs amount Tempe- HydrogenDesulf- Ex. Vol. (g) Time rature Pressure urization 4. 70:30 13.5 3 h 290° C. 300 psi 70 5. 70:30 13.5 l h 290° C. 300 psi 70 6. 70:30 13.5 45min 290° C. 300 psi 68 7. 70:30 13.5 30 min 290° C. 300 psi 59 8. 70:3013.5 10 min 290° C. 300 psi 50 9. 70:30 13.5 l h 240° C. 300 psi 10 10.70:30 13.5 l h 290° C. 500 psi 70 11. 70:30 13.5 l h 290° C. 100 psi 62

Further, the desulfurization was carried out at a reduced temperature of240° C., to understand the effect of temperature on the desulfurizationefficiency. Thus in Example 9, appropriate amounts of CBFO:Xylene(70:30) mixture was taken in the high pressure reactor. 13.5 g of Nametal was added and the reactor was pressurized with hydrogen to apressure of about 300 psig. The reactor was then heated to a temperatureof 240° C. with a residence time of 1 h. The reactor was cooled and theCBFO decanted and analyzed for the sulfur content. A desulfurizationefficiency of 10% was obtained in this case suggesting that the minimumtemperature where effective desulfurization can be carried out was 240°C.

These studies were further extended to understand the effect of partialpressure of hydrogen on the desulfurization efficiency.

In examples 10 & 11 different hydrogen pressures of 500 psig and 100psig were maintained. The temperature was raised to 290° C. with aresidence time of about 1 h. The reactor was cooled and the samplesdecanted and analyzed for sulfur content. It was observed that there wasonly a marginal improvement in the overall desulfurization efficiency athigh hydrogen partial pressures.

Thus, it was observed that the minimum temperature required for thedesulfurization reaction was about 250° C. Further, a residence time of1 h was found to be sufficient for optimum desulfurization to occur. Itwas also observed that the residence time could be further reduced byincreasing the sodium content above stochiometric or also by means ofincreasing the reaction temperature to above 300° C. The effect ofhydrogen partial pressure was not found to affect the desulfurizationefficiency significantly.

EXAMPLE 3

Desulfurization experiments were carried out in the presence and absenceof hydrogen and xylene. It was observed that the presence of xylene hasa significant impact on the processing as well as the by-productformation. Similarly, it was important to understand the effect ofhydrogen on the overall desulfurization process. Thus, in order to studythe effect of hydrogen and xylene individually and also in combination,the following schemes were investigated: example 12—desulfurization inthe presence of xylene and in the absence of H₂; example13—desulfurization in the presence of xylene and in the presence of H₂;example 14—desulfurization in the absence of xylene and in the absenceof H₂.

In case of example 12, 210 g of CBFO and 90 ml of xylene were taken inthe high pressure reactor. No hydrogen was added to the reactor. Forexample 13, 210 g of CBFO and 90 ml of xylene were taken in the highpressure reactor and about 300 psig of hydrogen was added to thereactor. For example 14, 210 g of CBFO was taken and no xylene orhydrogen was added. In all the examples 12-14, stoichiometric amount ofsodium metal were added. The reaction temperature was kept to 290° C.for a residence time of 1 h. Thus, after the reaction the samples werecooled and decanted for each of the cases. All schemes resulted in freeCBFO and sludge (Na₂S+CBFO) in varying proportions. The decanted CBFOwas weighed; the yields are given in TABLE 4.

TABLE 4 Ex. Composition Desulfurized CBFO yield (%) 12. No H₂ + Xylene72 13. H₂ + Xylene 78 14. No H₂ + No Xylene 54

It was observed that when xylene was used the CBFO yield was higher ascompared to when no xylene was added. Further, to reduce the sodiumcontent from the desulfurized oil, 5% mixture of acetic acid in xylenewas prepared. The acetic acid solution was added to the treated ordesulfurized oil. The mixture was then heated at 100° C. for 1 hr undervigorous stirring. The mixture was then allowed to cool down andfiltered. The treatment resulted in significant reduction in sodiumcontent from 2000 ppm to <50 ppm. Alternatively, the treatment ofdesulfurized oil can also be achieved by purging the oil with air underelevated temperatures. For this, 100 ml of desulfurized CBFO was takenin a glass air treatment tube and in this tube compressed air wascontinuously purged for a period of 30 minutes. This air reacts with theexcess of Na present in the oil to form a precipitated mass which can befiltered out. It was found that this treatment resulted in reduction inNa content by around 50% (from 2000 ppm to 900 ppm). Further to optimizethe treatment, same reaction was carried out at elevated temperature at50° C. It was found that the treatment resulted in significant reductionin Na content by around 96% (from 2200 ppm to 90ppm).

Experiments were performed to check the effect of heavy shear mixing inwhich samples were mixed at a low agitation mixing (200-300 rpm) with astirrer having blunt edged blades (made of Teflon/plastic) and sampleswere mixed under higher agitation speeds (700-800 rpm) mixing in a parrreactor with metal blades with relatively sharp edges. It was observedthat higher desulfurization was obtained when the agitator is capable ofbreaking the Na₂S particles that are formed and bringing new Na metalsurfaces in contact with the CBFO for further reaction.

TECHNICAL ADVANTAGES

A process for desulphurization of carbon black feed oil, as described inthe present disclosure has several technical advantages including butnot limited to the realization of the process does not require hydrogen;the process does not require high pressure conditions; the processreduces the loss of feed oil; the process gives a reduction in theasphaltene content of the petroleum oil by >50%; the process improvesthe viscosity of the desulphurized oil to <200 cP; the process reducesthe residual sodium content to <10 ppm; the process enhances theprocessing and handling conditions of the CBFO; the process provideseasy filtration and separation of the desulfurized oil and by-productsthereof; and the process is safe as it lowers the density of oil incomparison with sodium metal.

Throughout this specification the word “comprise”, or variations such as“comprises” or “comprising”, will be understood to imply the inclusionof a stated element, integer or step, or group of elements, integers orsteps, but not the exclusion of any other element, integer or step, orgroup of elements, integers or steps.

The use of the expression “at least” or “at least one” suggests the useof one or more elements or ingredients or quantities, as the use may bein the embodiment of the invention to achieve one or more of the desiredobjects or results.

Any discussion of documents, acts, materials, devices, articles or thelike that has been included in this specification is solely for thepurpose of providing a context for the invention. It is not to be takenas an admission that any or all of these matters form part of the priorart base or were common general knowledge in the field relevant to theinvention as it existed anywhere before the priority date of thisapplication.

The numerical values mentioned for the various physical parameters,dimensions or quantities are only approximations and it is envisagedthat the values higher/lower than the numerical values assigned to theparameters, dimensions or quantities fall within the scope of thedisclosure, unless there is a statement in the specification specific tothe contrary. Wherever a range of values is specified, a value up to 10%below and above the lowest and highest numerical value respectively, ofthe specified range, is included in the scope of the disclosure.

While considerable emphasis has been placed herein on the specific stepsof the preferred process, it will be appreciated that additional stepscan be made and that many changes can be made in the preferred stepswithout departing from the principles of the disclosure. These and otherchanges in the preferred steps of the disclosure will be apparent tothose skilled in the art from the disclosure herein, whereby it is to bedistinctly understood that the foregoing descriptive matter is to beinterpreted merely as illustrative of the disclosure and not as alimitation.

1. A process for desulphurization of petroleum oils, said processcomprising the following steps: diluting petroleum oil with ahydrocarbon organic solvent selected from the group consisting ofalkanes, alkenes, cyclic alkenes and alkynes, to obtain an oil-solventmixture, wherein the organic solvent concentration in the oil-solventmixture is in the range of 0.1-70%; transferring the oil-solvent mixtureto a reactor vessel; adding solid sodium metal to the oil-solventmixture in the reactor vessel, wherein the sodium concentration isbetween 0.1-20% of the petroleum oil concentration; reacting theoil-solvent mixture with sodium at a temperature in the range of240-350° C. and a pressure in the range of 0-500 psig for 15 minutes-4hours under mixing to obtain a resultant mixture; cooling and settlingthe resultant mixture; and decanting the cooled mixture and filteringthe decanted solution of desulfurized petroleum oil.
 2. The process asclaimed in claim 1, wherein the hydrocarbon organic solvent is selectedfrom the group consisting of n-hexane, cyclohexane, heptane, pentene,hexene, heptene, octene, toluene and xylene.
 3. The process as claimedin claim 1, which includes the step of purging the reactor vessel withhydrogen gas at a pressure in the range of 0-500 psig.
 4. The process asclaimed in claim 1, which includes the step of separating the organicsolvent from desulfurized petroleum oil by distillation.
 5. The processas claimed in claim 1, which includes the step of mixing sodium with theoil-solvent mixture in the reactor vessel by using high shear mixing bymeans of a mixer selected from an inline mixer, a mechanical mixer, apump around loop and an ultrasonic mixer.
 6. The process as claimed inclaim 1, which includes the step of removing residual sodium metal by:treating the desulfurized petroleum oil with 0.1-10% carboxylic acid inan organic solvent at a temperature in the range of 50-150° C. for 30minutes to 90 minutes under vigorous stirring; and filtering theresultant mixture to obtain desulfurized petroleum oil having sodiumcontent between 10-50 ppm.
 7. The process as claimed in claim 6, whereinthe carboxylic acid is selected from acetic acid, formic acid andpropionic acid.
 8. The process as claimed in claim 6, wherein theorganic solvent is selected from alkanes, alkenes, cyclic alkenes,alkynes and alcohol.
 9. The process as claimed in claim 6, wherein theorganic solvent is xylene.
 10. The process as claimed in claim 1, whichincludes the step of removing residual sodium metal by purging thedesulfurized petroleum oil with air at a temperature in the range of30-150° C.